The present invention relates to a photographic objective for single-lens mirror reflex cameras with a preselector iris system and with an automatic diaphragm comprising a spacially fixed leaf support ring supporting the diaphragm leaves as well as a leaf guide ring rotatable relative to the leaf support ring, and wherein, after a picture is taken, the automatic diaphragm opens to its largest value depending on the hinge motion of the reflex mirror.
After a picture has been taken, the reflex mirror performs an advance, that is a motion larger than required for opening the diaphragm to the full value. The advance assures that the hinge motion of the reflex mirror is sufficient to reach the largest opening value of each objective employed with the mirror reflex camera. The advance has to be compensated for in order to avoid damage occurring in the region of the diaphragm.
In order to compensate for the advance, it is known to provide the guide grooves of the leaf guide ring such that, on one hand, they cause a rapid closing of the diaphragm and, on the other hand, they effect little or no further motion of the diaphragm leaves after the leaves reach the largest opening which could be achieved under control of the diaphragm lever on the side of the camera. Such overflow curves at guide grooves can only be realized with objectives having a short or average focusing length without resulting in disadvantages relative to delays in the closing of the diaphragm. In contrast, objectives with longer focusing lengths and with openings relatively large with respect to this are furnished with leaf guide rings. The guide grooves of the leaf guide rings in fact allow a rapid closing of the diaphragm before the start of the camera shutter operating cycle, but they permit a compensation of the advance of the reflex mirror only under certain technical preconditions.